There are many reasons to study Leviticus, but time and space don't allow me to probe them all. I will, however, share one good reason: because in his first epistle, the apostle Peter relies on it to explain what holiness is.
When a New Testament writer uses an Old Testament reference, we should stop and ask ourselves why. How is he using that Old Testament citation to build his teaching? What does the reference say about the unity of the two testaments? It's a time in our study when we must stop and think about what lies behind the author's purpose.
In the midst of an exhortation to his readers to prepare themselves for action, and to set their hopes on the revelation of Christ, Peter tells them to be holy in their conduct (I Pet. 1:13-15). And why ought they to be holy? Because God is holy. To lend support to his exhortation, he quotes Leviticus 19:2. That phrase "be holy" occurs a few times in Leviticus.
Leviticus 11 deals with the purity laws referring to food. At the end of this passage, the writer concludes by giving a call to the people to consecrate themselves for holiness by avoiding that which is unclean. The reference in Lev. 19:2 opens a section within the "Holiness Code" which encompasses chapters 17-24. In Lev. 19, the writer is calling people to demonstrate holiness in their relationships with other people. Later in Lev. 20:26, the writer adds the reminder that their holiness is expected because of what God has done for Israel, specifically, deliverance from Egypt (Ex 19:4-6). Holiness is in response to a covenant which establishes them as "kingdom of priests and a holy nation" (Lev. 19:6), the same phrases which Peter uses in his letter. A call to holiness is part of the covenant God has made with them. So, how does holiness in Leviticus relate to Peter's audience, and ultimately, to us?
Peter's use of Leviticus is one of many references which create in this letter an overwhelmingly Jewish theme. Phrases like "the Diaspora," (I Pet. 1:1), "a chosen race, a royal priesthood, a holy nation" (I Pet. 2:9), and the many direct citations from the Old Testament (1:15; 1:24-25; 2:6-8;3:10-12; 4:18) sound as if Peter is talking to Jews. However, scholars are agreed that Peter wrote to Gentiles. So, why is Peter using Old Testament language with Gentiles?
Peter is drawing a parallel between the Jews and the new covenant believers. While there is change in their relationship to the law, the nature of holiness has not changed. The holiness that has been established by God with his covenant people Israel is the same holiness that is expected of the new covenant people. Holiness was visible among the Jews in a lifestyle that was separate from their neighbours. They were to stand out among the pagan nations, refuse to adopt their ways, and remain faithful to their covenant God. Peter is saying that it is no different for his readers, and by extension, Christians today: we must live separate from the surrounding culture, not become like it. This was an especially appropriate message to these Gentile believers who were living with persecution and suffering (I Pet. 1:6; 4:12). The response to trials is to live as a holy people. While holiness is attained through faith in Christ, it is visible by a consecrated, separate life.
Perhaps Peter could have just come out and said this without referring to Leviticus, but by doing so, he not only gives credibility to his teaching by appealing to the Old Testament Scriptures, but he roots his teaching in the past, emphasizing the continuity of the Old and New Testaments. God's purposes have not changed. Today, with two thousand years of Christian history behind us, we take for granted the equal authority of the Old Testament and New Testament Scriptures. In the early days of the church, it was not like that. The new believers had to be shown this continuity, and ultimately, the only Scriptures the New Testament writers had were the Old Testament. Basing their teaching on Scripture meant the Old Testament.
Leviticus is probably not the kind of literature we read every day. It sounds strange to our ears. Maybe we groan inwardly as we consider reading it, but when we look at it retroactively, from where we are today in the new covenant, we can see its importance. If the Old Testament Scriptures were used by the New Testament writers, we ought to pay attention to them; even Leviticus. Next time you see a New Testament author quote the Old Testament, take a moment to ask why. It will enrich your study.